1. Field of the Invention
The present invention relates to a light emitting device that excites a fluorescent body with near-ultraviolet light and emits light.
2. Description of the Related Art
A conventional light emitting device is disclosed in JP-A-2010-86815. This light emitting device includes a light source and a plurality of fluorescent members. The fluorescent members have fluorescent bodies that are excited by excitation light to emit red light, blue light and green light, respectively, and are provided on a heat transmission member. The light source is formed with a light emitting diode or a laser diode, and emits, as the excitation light, ultraviolet light having a wavelength shorter than the band of the wavelength of the light emitted by the fluorescent bodies. In general, the fluorescent member is formed by dispersing the particles of the fluorescent body into a sealant such as a resin or an inorganic glass.
In the light emitting device configured as described above, the excitation light formed with the ultraviolet light emitted from the light source is applied to the fluorescent members. The fluorescent bodies of the fluorescent members are excited by the excitation light, and thereby emit red light, blue light and green light, respectively. The light emitted from the fluorescent members is combined, and thus intended light is emitted
When a light emitting device is used in an application where illumination light having a high brightness is required, a high-power laser diode can be used as a light source. When excitation light emitted from a light source is not utilized as illumination light, it is preferable to increase the rate of absorbing the excitation light by the fluorescent members and thereby enhance the efficiency of light emission of the fluorescent members.
When the high-power laser diode is used as the light source, the density of excitation of the emitted light is increased, and thus the fluorescent body produces heat. In the conventional fluorescent member described above, the heat produced by the fluorescent body is transmitted though the sealant and is dissipated from a substrate. Here, when the thickness of the sealant of the fluorescent member is increased so as to enhance the rate of absorbing the fluorescent member, and thus a content of the fluorescent member is increased, since the fluorescent body on the emission surface side is separated from the substrate, the heat dissipation of the fluorescent member is disadvantageously degraded. This causes the temperature of the fluorescent body to be increased, and thus the efficiency of light emission is reduced and a light emission portion is degraded. Moreover, since temperature quenching is different according to the type of fluorescent body, variations in chromaticity may occur.
Although, in the conventional fluorescent member described above, the fluorescent member is moved to change the position of application of the excitation light, and thus the increase in the temperature of the fluorescent body is reduced, a drive portion for moving the position of the application is required, with the result that disadvantageously, the consumption power is increased and its configuration is complicated.
On the other hand, since the particles of the fluorescent body are dispersed into the sealant, it is difficult to increase the content of the fluorescent body while the sealant is thin.